1. Field of the Invention
The invention relates to means for indicating whether a signal is fluctuating or stable. Particular embodiments of the invention relate to means for indicating when the output of a measuring instrument has stabilized.
2. Description of the Prior Art
In many measuring instrument applications, the instrument's output reading is of interest only when it has stabilized after an initial settling period. The settling period may be required either because the parameter being measured requires a certain time to stabilize or because the measuring instrument has a slow response time. An example of the former is the measurement of a parameter of a chemical mixture, such as pH, wherein the parameter is of interest only after some chemical reaction has proceeded to completion or has reached an equilibrium point. An example of the latter is a typical pH meter whose output reading requires a noticeable amount of time to asymptotically attain its correct value. Another example is a weighing machine which typically experiences mechanical vibrations for a short time after an object is placed on the machine for weighing.
The need for a means to detect when an instrument reading has stabilized has been recognized for some time. However, previously known means for doing so typically sample the instrument reading at fixed points in time and then test whether successive samples differ from each other. If the instrument reading happens to fluctuate between sampling times, the fluctuations may escape detection, causing the instrument reading to be erroneously identified as stable.